A relatively large number of patients are suffering dental injuries during transoral medical procedures. By way of example, a transoral procedure may be such as, but not limited to, an intubation or a rigid or flexible endoscopic procedure. During an intubation, an intubation laryngoscope 164, consisting of a curved, or straight, blade 166 is inserted into a patient's mouth 168 and throat 170 to examine the larynx, or for inserting a tube through it, as shown in FIG. 3. The patient 172 is in a supine position and is given induction anesthesia and muscle relaxants to facilitate the procedure. An anesthesiologist places the blade 166 deep on the patient's tongue, after which the lower jaw 174 is lifted to get full visualization of the voice box and the trachea, into which an endo-tracheal tube 176 may be inserted. During this process, the intubation laryngoscope 164 may need to be tilted for optimal visualization, thus applying pressure to the front teeth of the upper jaw (maxilla). This procedure is generally depicted in FIG. 3.
The applied pressure causes the central incisor teeth to become loaded with several Newtons (N) of force, sometimes as high as 87 N. It comes as no surprise then that studies have found the most frequently damaged teeth during an intubation are the central incisor teeth. Given the variability in both the state of healthiness of the dentition of a given patient undergoing an intubation procedure and the magnitude of force applied to achieve medical instrument entry to the trachea, a range of damage can occur to one or more teeth. Below is a chart briefly describing the damage ranges by class and description.
Damage RangesClassDescriptionIFracture into the enamel layerIIFracture into the dentinal layerIIIFracture into the pulp of the toothIVFracture of the root of the toothVSubluxation of a tooth (a partial dislocation)VIAvulsion of a tooth (a tearing away of a bodypart accidently or surgically)
Prior art dental appliances exist to protect the dentition of a patient during transoral medical procedures from damage or injury. Yet, dental injuries are reported in about 1.5% of intubations and are the major reason for law suits against anesthesiologists. Despite availability to such appliances, anesthesiologists and nurses, MDA's and CRNA's, respectively, tend not to use them for two major reasons: Firstly, a major disadvantage with existing dental appliances is that they fit extremely poorly onto the dentition. As a result of poor fit, the prior art appliances rarely remain in place on the dentition, and often become dislodged from the dentition during a transoral procedure or intubation. If the appliance is not in the proper position on the dentition, it can obstruct the view of the voice box thereby making it difficult to safely guide an endotracheal tube into the patient's larynx and further down into the trachea. Of course, if the appliance also does not remain in place, it will not protect the dentition. Intubation is not the only transoral procedure in which a patient's dentition is at risk for damage. Ear, nose and throat physicians, gastroenterologists and thoracic surgeons often use specialized instruments, such as a rigid laryngoscope, esophagoscope, or bronchoscope, during transoral procedures during which they apply pressure on the dentition and can cause damage as well.
Secondly, these prior art appliances are typically made of a soft, highly compressible polymer that often breaks down under pressure by undergoing extensive plastic deformation and even fracture, and therefore do not protect the dentition very well. The typical thermoplastic polymeric material used to construct these prior art appliances is ethylene vinyl acetate (EVA) which is well known to be a mechanically soft material. An indirect assessment of mechanical softness/hardness of a material is given by the basic material property, the Young's Modulus. A typical EVA (30% vinyl acetate) polymer often used to construct a prior art appliance has a Young's Modulus of 0.015 GPa. In contrast, the preferred polymer for construction of the subject invention appliance is polycaprolactone (PCL) which has a Young's Modulus that is two orders of magnitude greater at 1.2 GPa. The much greater Young's Modulus indicates a much stiffer material, essentially a harder material.
A comparatively much lower Young's Modulus also indicates a lesser capability to absorb and distribute force over an area. By definition the Young's Modulus is the ratio of the stress (force per unit area) applied in the axial direction to the strain, or deformation, incurred in that direction. The higher Young's Modulus of 1.2 GPa for PCL clearly indicates that the PCL material can absorb and distribute on the order of 100 times more force over the equivalent area than the EVA material, and this is before the onset of permanent material damage. Intuitively, the better dental protecting appliance is certainly the one that has a greater capacity to absorb force over an area, i.e. the dentition, in both the horizontal and axial directions.
Examples of appliances intended for the protection of teeth during transoral procedures or intubation include U.S. Pat. Nos. 4,112,934, 4,640,273, U.S. Patent Application Publication 2007/0235040, and U.S. Patent Application Publication 2008/0156331.
In view of the disadvantages of the prior art appliances, it would be desirable for a dental appliance to stay in place during any transoral procedure or intubation, to permit a clear view of the larynx and the tracheal inlet and to significantly diminish and/or re-direct forces applied to the dentition to prevent dental damage.